The basic image-forming process of silver halide photography comprises the exposure of a silver halide photographic element to actinic radiation (for example, light or X-rays), and the manifestation of a usable image by the wet, chemical processing of the element. The fundamental steps of this processing entail, first, treatment of the photographic element with one or more developing agents wherein some of the silver halide is reduced to metallic silver. With black-and-white photographic materials, the metallic silver usually comprises the desired image. With color photographic materials, the useful image consists of one or more images in organic dyes produced from an oxidized developing agent formed where silver halide is reduced to metallic silver.
To obtain useful black-and-white images it is usually desirable to remove the undeveloped silver halide, and to obtain useful color images it is usually desirable to remove all of the silver from the photographic element after the image has been formed. In black-and-white photography the removal of undeveloped silver halide is accomplished by dissolving it with a silver halide solvent, commonly referred to as a fixing agent. In color photography the removal of silver is generally accomplished by oxidizing the metallic silver, and dissolving the oxidized metallic silver and undeveloped silver halide with a fixing agent. The oxidation of metallic silver is achieved with antioxidizing agent, commonly referred to as a bleaching agent. The dissolution of oxidized silver and undeveloped silver halide can be accomplished concurrently with the bleaching operation in a bleach-fix process using a bleach-fix solution, or subsequent to the bleaching operation by using a separate processing solution containing a fixing agent.
It is highly desirable to process a photographic element as rapidly as feasible, and a shortened process compared to ones known in the art is highly desired. Shortening the silver removal step, which consumes a large amount of the total process time, is one manner in which to shorten the overall processing time. Juxtaposed to the desire for an accelerated process is the desire for, and the need for, photographic elements and processing solutions that require lower chemical usage and that generate less polluting chemical waste.
A wide variety of fixing agents and silver solvents are known. Such materials form relatively stable and soluble reaction products with silver ion or silver halides. Such agents include, for example, alkali metal and ammonium thiosulfates, thiocyanate salts, sulfites, cyanides, ammonia and other amines, imides as described in U.S. Pat. No. 2,857,274; thiols as described in U.S. Pat. Nos. 3,772,020 and 3,959,362; mesoionic 1,2,4-triazolium-3-thiolates as described in U.S. Pat. No. 4,378,424 and other mesoionic heterocyclic thiolates as described in European Patent Application 431,568; thioureas, thioacids, and thioethers as described in German Offen. 2,037,684 and U.S. Pat. Nos. 2,748,000; 3,033,765; 3,615,507; 3,958,992; 4,126,459; 4,211,559; 4,211,562; 4,251,617; and 4,267,256; phosphines as described in U.S. Pat. No. 3,954,473; and concentrated halide solutions as described in U.S. Pat. No. 2,353,661.
Thiosulfate salts are generally preferred as fixing agents because they are inexpensive, highly water soluble, non-toxic, non-odorous, and stable over a wide pH range in the fixer bath. Furthermore, thiosulfate salts form very stable, water soluble reaction products with both silver ion and with silver halides. Sulfite salts are practical fixing agents for the same reasons as thiosulfate mentioned above, except sulfites are not useful for the fixing of silver bromide or silver iodide containing materials. Sulfite salts are effective fixing agents for high chloride elements, as indicated, for example, in U.S. Pat. No. 5,171,658. On a mole for mole basis, sulfites are not as rapid in fixing action as thiosulfates, but sulfites contribute less sulfur waste, less BOD (biochemical oxygen demand), and less COD (chemical oxygen demand) to photographic processing waste than do thiosulfates. Therefore, there is a need to improve the fixing speed of sulfite fixing agents for silver chloride photographic materials so that the environmental advantages of sulfites can be realized.
Thioether compounds have been reported to improve bleaching effectiveness when present in bleach or bleach-fixing baths (for example, British Patent 933,008; U.S. Pat. Nos. 3,241,966; 3,767,401; 4,201,585; 4,695,529; 4,804,618; 4,908,300; 4,914,009; 4,965,176; and 5,011,763; and unexamined Japanese Patent Application JP 02-44,355 A). These references do not disclose the use of thioethers as fix accelerators.
U.S. Pat. No. 4,960,683 of Okazaki et al. describes a method for processing black-and-white photosensitive materials comprising fixing a developed black-and-white spectrally sensitized photographic material in the presence of an aliphatic thioether compound and/or a heterocyclic thiol or thiolate compound. There is no indication that such compounds are useful with sulfite fixing solutions.
The use of ammonium thiocyanate, thiourea, or a thioether (e.g. 3,6-dithia-l,8-octanediol) to accelerate fixing by ammonium thiosulfate is mentioned in U.S. Pat. No. 5,002,861. There is no indication that these compounds are useful with other fixing agents, such as sulfite.
SIR H953 describes a method of processing color photographic materials in which thioether-containing compounds are present in a fixer bath which immediately follows a bleaching bath containing ammonium 1,3-diaminopropanetetraacetatoferrate(III) as the bleaching agent. The reported result of such a process is the improved bleaching of the developed silver in the photographic material. There is no mention of using such compounds with a sulfite fixing agent.
There remains a need for materials or methods that increase the speed of fixing of silver chloride photographic recording materials. Further, there remains a need for materials or methods that increase the fixing speed of sulfite fixers, so that improved processing ecology can be achieved.